The main objective of this research is to increase our understanding of charge transfer across biological interfaces. The second aim is to test our theory of electron transfer across interfaces. We will use the recombination kinetics of the photo-formed charged pair to probe the interfacial region. We propose to extend the present time resolution of our measurements (200ns) to study relaxation in the "double layer" atmosphere. We will measure distance and orientation effects on these reactions, predicted by our theory, by the use of oriented donors and acceptors and by photoselection. We will extend these studies to cytochromes and other biological components to learn of orientations and distances in reactive complexes. By coupling these electron transfer reactions to protons, we will study proton transfer across these interfaces, and so duplicate bioenergetic coupling. We will use these electrochemical techniques on bacteriorhodopsin to obtain information on the mechanism of the proton pump.